Need ideas to test stereo power amps

[luthierwnc]

Hi All,
Of all my requests, this may be the lamest. 

I have two Samson Servo-200 stereo power amps.  Both power-up, the fans cut on, looks like they work.  But I can't get a sound out of them.  My idea was to use one of them as a stereo FX driver by taking the speaker-feed from a tube amp, running it through a Radial Cab-Link box into a Line 6 HX Effects processor and then into the Samson which pushes two small 1x10 cabs. 

According the the manual the amp needs +4dBu to power correctly.  I can't, for the life of me, determine if I'm doing this right.  The Line 6 works fine before the amp.  I've tried running the Cab-Link into one of the mono inputs.  The Cab-Link works fine for the speaker and I've fiddled with the line-out level pot. 

Since I don't know how to measure the output from the Line 6 (doesn't work with a Boss GP-10 either) in decibels, I can't be sure I'm even sending enough juice to the stereo amp.  Might need a preamp of some kind.  According the the Samson manual, TS cables should work for the balanced 1/4" inputs but not as well as TRS.  Anything noise at all would be an improvement but I might solder an unbalanced connector on the input cables just to see if that makes a difference.
Any ideas how to slap one of these bad boys into action would be a help.  Thanks, sh

[PRR]

> According the the manual the amp needs +4dBu to power correctly.

No. You need +4 to get the full 200 Watts you paid for. But to test you would be pleased with a part-Watt, down like -30dBu. In fact a hot guitar should make audible sound in the house. Your iPod/CellFone with 1/8" to 1/4" adapter should make music.

What is that unlabeled 8-knob box in the center of your sketch? If non-trivial, where is its manual?

Why do you need a Cab-Link for testing?

Sampson Servo-?00 manual  http://www.samsontech.com/site_media/legacy_docs/Servo23600_ownman_v1_1.pdf

NOTE "Protection" on page 7/9.
Initial power-up:
• Overheating:
• Severe overcurrent conditions:
• Shorted speaker cables:
• Output impedance drops below 4 ohms:
• DC voltage detected at speaker output:

[luthierwnc]

Thanks PRR
I'm mostly trying to see if these things work.  I got them cheap in hopes one of them would function.  Both power-up but neither of them lights the protection LEDs or make the click after five seconds as mentioned on page 7.  On one the LED's flash from hot to low when I power down.  Inside they are clean with no sign of heat damage.  I didn't see a reset breaker internally.  It wouldn't cause lasting trauma to get a new amp with a warranty - probably not the same brand.
The black box is the Line 6 but I've tried with a Boss GP-10 with the same result.  Both processors between a guitar and amp work fine.  So does the Cab-Link into the Line 6 into an amp.  For grins I'll see if I can't drive the Samson with the little headphone DAC on my computer when the household is already awake.  I've got a smaller stereo amp in the shop that I can sub after some untangling.  I'll also give Samson a call.

Looks like a dead-end but thought I'd check.  Cheers, sh
PS  8-ohm cabs

[pdf64]

If the speaker protection relay doesn’t actuate a few seconds after power up, then the amp is probably in safety / protection mode.
If they’re secondhand, that may be why you got em cheap.
Check that there isn’t any VDC on the amp side of the relay.
And any internal fuses, perhaps soldered to the board, rather than user replaceable.
And that the load isn’t shorting the amp’s output somehow.
Beyond that it can get tricky, if there’s VDC the best chance of success may be to replace all semiconductors, which can be more trouble than it’s worth.

[luthierwnc]

Thanks PDF64,
I've got 50 bucks in the pair --  lost more than that many times.  I'll call Samson to see if they have a; "Oh, you just toggle ..."  If not, these go in the graveyard.  Cheers, sh

[luthierwnc]

Update:  I disassembled my shop stereo Amp100vs and lopped the TS plugs off a couple speaker cables.  It worked flawlessly so the Samsons are either toast or need attention.  Thanks all for your input and wish me luck on the next piece of kit.  If any little stereo amps come to mind in place of the Servo-200, I'd enjoy hearing your thoughts.  50-watts a side is probably plenty.  sh

[pdf64]

For a wet only satellite rig, I just use a 25W solid state combo I got for a penny on ebay. After a squirt of cleaner lube in its pots, and reflow of the solder joints around the pots, jacks etc, it works great.

[luthierwnc]

That's what I thought I was doing with the Samson.  I'll watch Ebay for unloved amps.  sh